Three-Level Inverter Balance Circuit for Midpoint Voltage Control
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Solution Overview
Problem
Conventional power conversion devices rely solely on software algorithms to regulate midpoint voltage in off-grid mode, which are ineffective under small load conditions and lose regulation capability with rectified half-wave loads, limiting their ability to balance voltage.
Innovation Solution
A power conversion device comprising a three-level inverter, balance circuit, and bidirectional DC-DC converter, controlled by a controller to maintain equal voltages across capacitors, ensuring reliable midpoint voltage balancing across various load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If software algorithms are used to regulate midpoint voltage balance, then the system can operate in off-grid mode, but the regulation capability is limited under small load conditions and rectified half-wave loads
Solution Approach 1:
The patent introduces a balance circuit as an intermediary component between the DC link capacitors to actively regulate voltage balance. This balance circuit includes switching elements that can transfer charge between capacitors, providing a dedicated mechanism for voltage balance regulation that works independently of the main power conversion switches. This intermediary structure ensures reliable midpoint voltage balancing under all load conditions, including small loads and rectified half-wave loads where conventional software algorithms fail.
2Device complexity
If only software algorithms are used for voltage regulation, then the device complexity is low, but the regulation effect is insufficient under small load currents
Solution Approach 1:
The balance circuit serves as a specialized intermediary component that supplements the control system. It includes dedicated switching elements and control logic specifically for voltage balance regulation, separating this function from the main power conversion control. This modular approach maintains reasonable device complexity while significantly improving voltage regulation effectiveness under all operating conditions.
Solution Approach 2:
The balance circuit automatically regulates voltage balance between capacitors through its controlled switching elements, providing self-service voltage balancing without requiring complex software algorithms to manipulate main power switches. The circuit monitors capacitor voltages and activates balance operations only when needed, improving regulation effectiveness while maintaining simple control structure.
Data Source
AI summary
A power conversion device and a control method thereof are provided. The power conversion device includes a three-level inverter, positive and negative DC terminals, first and second capacitors, a balance circuit, a bidirectional DC-DC converter and a controller. The three-level inverter has two DC terminals coupled to the positive and negative DC terminals respectively. Two terminals of the first capacitor are coupled to the positive DC terminal and a capacitor midpoint respectively. Two terminals of the second capacitor are coupled to the capacitor midpoint and the negative DC terminal respectively. The balance circuit is electrically connected between the positive and negative DC terminals and has a neutral terminal electrically connected to the capacitor midpoint. The bidirectional DC-DC converter is electrically connected to the DC terminals. The controller controls the balance circuit according to two capacitor voltages across the first and second capacitors respectively to keep the two capacitor voltages equal.